A. Field of the Invention
This invention pertains to apparatuses and methods regarding a clutch mechanism that can replace a torque converter and more specifically to apparatuses and methods regarding a clutch mechanism using a pair of clutches that provides a starting clutch and a gear splitting feature for use in doubling the number of gear ratios supplied by an automatic transmission.
B. Related Background Art
The use of a torque converter between an automotive engine and an automatic transmission is well known in the art. Torque converters are fluid couplings that permit the engine drive shaft to rotate somewhat independently of the automatic transmission. As a result, torque converters permit the automobile to start motion and also to come to a complete stop without stalling the engine. Torque converters thus work well for their intended purpose.
Torque converters, however, have disadvantages. One disadvantage is that torque converters are known to be relatively inefficient. In particular, torque converters generally provide relatively poor fuel economy—although this can be improved with the addition of a lockup clutch. The lockup clutch locks the torque converter turbine to the torque converter pump when the rotational speed is sufficiently high thereby eliminating slippage and improving efficiency.
It is known to provide dual clutch systems in place of torque converters in order to minimize these disadvantages. U.S. Pat. No. 3,938,631 to Smith provides a gearing system with speed responsive starting clutches. This gearing system is used to eliminate the conventional fluid drive unit in a transmission drive arrangement having input clutches for connecting the fluid drive unit to automatic shifting planetary gearing. A torque converter is eliminated from the drive arrangement, and the existing input clutches of the drive arrangement are used as starting clutches. However, Smith does not provide a gear splitting feature for use in doubling the number of gear ratios supplied by the transmission.
U.S. Pat. No. 6,491,149 to Kundermann et al. provides a double clutch apparatus positioned in a drive train of a motor vehicle between a drive unit and a transmission. The double clutch apparatus has a first clutch associated with a first transmission input shaft and a second clutch associated with a second transmission input shaft. Both transmission input shafts are used to transmit torque between the drive unit and the transmission. However, Kundermann does not provide a gear splitting feature for use in doubling the number of gear ratios supplied by the transmission.
U.S. Patent Application Pub. No. US 2002/0086766 to Hayashi et al. provides a starting clutch usable in place of torque converter in an automatic transmission. The starting clutch includes wet first and second clutches, a planetary gear, and a damper. However, Hayashi et al. does not provide a single transmission input shaft separately rotatable by either clutch independently.
U.S. Patent Application Pub. No. US 2003/0130082 to Janson provides two clutches, preferably wet friction clutches, to allow an automatic transmission driven vehicle to start up from a stop and remain stopped while in gear without a torque converter. However, Janson does not provide a single transmission input shaft separately rotatable by either clutch independently.
Aside from the torque converter issues just discussed, there is a general push in the automotive industry for an increase in the number of gear ratios available from the transmission. Often three to five forward gears are no longer considered sufficient because there is an increasing desire for six to eight forward gears. One solution is to design and build larger and more complex transmissions. However, this solution has the disadvantage of adding undesirable weight and cost to the manufacture of a transmission.
What is needed is a clutch mechanism using a pair of clutches that serves as a starting clutch and that provides a gear splitting feature for use in doubling the number of gear ratios supplied by the automatic transmission. In this way the disadvantages known in the art can be overcome in a way that is better, more efficient and that provides better overall results.